Chalcogenide glasses and films are promising materials for use as solid electrolytes. These materials are used for different applications, such as optical and photonic materials (laser, fiber optics, and optical lenses for infrared transmission), rewritable optical discs, and non-volatile memory devices such as phase change memory. Currently they have been used in next generation non-volatile solid state memory such as electrochemical metallization memory cells (ECM) and conductive bridging random access memory (CBRAM). CBRAM works by sandwiching a metal chalcogenide solid electrolyte between an inert cathode and sacrificial anode. When a potential is applied, metal ions from the sacrificial anode migrate into the solid electrolyte and form a “conductive” bridge to the other electrode creating an electrical short. The resultant change in resistance can be a basis for a memory element. Several metal chalcogenides have shown promise as a solid state electrolyte in this application including, germanium chalcogenides (sulfide, selenide, and telluride compounds), arsenic chalcogenides compounds (sulfide, selenide, and telluride compounds), and molybdenum chalcogenides (sulfide, selenide, and telluride compounds). These compounds can be doped with several ions including Ag+, Li+, and Cu+2. These materials have been shown to better survive the high temperature of back-end-of-line processing in integrated circuit manufacture. The materials in various forms also have uses in many other applications including inorganic photoresists, photonic devices, fiber optics, chemical sensors, optoelectronics and waveguides. The glasses and films may be useful in smart cards, integrated circuits, inorganic photoresists, transistors, field emitters, solid state lithium ion batteries. The glasses and films may also be useful in medical applications, photocatalytic applications, hydrogen evolution, and value added fuel generation.
There are several methods available for the preparation of chalcogenide glasses and films, particularly germanium sulfide glasses and molybdenum sulfide glasses, including sol-gel synthesis, chemical vapor deposition, and laser assisted chemical vapor deposition. Metal ion doping on chalcogenide glasses can be performed by conventional methods such as chemical vapor deposition, photo doping, and electrochemical methods. These methods have limitations because they require the use of high temperature, corrosive gases, or long processing time frames. Germanium sulfide and molybdenum sulfide formation by sol-gel synthesis involves the use of H2S gas with specialized equipment (stainless steel high pressure reactors) to keep the sample out of contact with the air and the reaction can take place for several days to month. Chemical vapor deposition involves the use of specialized equipment at high temperatures, around 400° C. to 700° C., as well as H2S gas. Deposition during CVD occurs at a rate of about 12 μm/hr. Furthermore, in conventional silver doping techniques, it is difficult to estimate the concentration of Ag+ doped on the system.
Other techniques such as evaporation, sputtering, and ablation in general suffer from difficulties associated with the incorporation of impurities or non-stoichiometry, which degrade the properties of the chalcogenide glass. The synthesized products are not pure or uniform and depend upon the targets materials used in the synthesis. These options also have a limit to the speed, cost, and scale at which they can be produced.